Various attachments and guides have been provided in the prior art to enable portable chain saws to cut boards and lumber from logs without the use of a sawmill. It is an object of the present invention to overcome difficulties encountered with the prior art attachments and guides.
U.S. Pat. Nos. 3,051,203 and 3,225,799 to Ernest A. Hayden show two types of attachments which use rollers and wheels which cooperate with a guide nailed to the top of a log for guiding movement of the chain saw. Attachments of this type are expensive because of the guide rollers and bearings required and have proved to be awkward and unsatisfactory in use because of the problem caused by chips and sawdust which get between the rollers and the guiding surface of the log which causes irregular cuts and a consequent uneven surface on the cut lumber.
U.S. Pat. No. 3,864,830 to Jesse E. Haden and U.S. Pat. No. 4,070,757 to Elof Granberg et al disclose attachments for adapting chain saws to cut lumber from logs. Both of these examples of the prior art rely on a guide such as a two-by-four board nailed to the log to the cut and along which the chain saw traverses in making the initial cut in the log. This is objectional because the operator must necessarily have a long straight board in addition to the attachments connected to the saw bar of the chain saw. In both Haden and Granberg the attachments are clamped to the saw bar as opposed to being rigidly connected as by bolts. The clamping of the attachments to the saw bar as disclosed in Haden and Granberg is hazardous because the vibration of the chain saw tends to loosen the clamping mechanism and the rapidly rotating saw chain may be accidently moved against the metal attachments causing flying shrapnel and consequent danger of injury or death.
U.S. Pat. No. 3,965,788 to Elof Granberg discloses a lumber making attachment for a portable chain saw which is also attached as by clamping to the saw bar of the chain saw and also relies on the attachment of a guide directly to the log to make the first cut in the log. The Granberg disclosure is objectionable for the reasons previously given.